This invention relates generally to optical systems for interferometry, and more particularly, to a system for converting a circular ring spectrum of the type generally produced by an interferometer, such as the well-known Fabry-Perot interferometer, to a linear pattern which is similar to that produced by a conventional spectroscope, and which can be scanned using relatively inexpensive and simple commercially available detection devices.
The commercial success of linear spectroscopic instruments, such as grating spectrometers where the spectral information is presented as a linear pattern, has resulted in significant advances in the production of simple array detectors which assist in the automatic analysis of the spectral information. However, such is not the case in the field of interferometry. Interferometers have suffered in the commercial market as a result of the lack of simple array detectors which are capable of being applied to the circular geometry of the typical interference pattern.
Many interferometers used for testing and spectral analysis produce information in the form of circular rings or fringes. Such devices are employed in the laboratory, in geophysical observations, and in astonomical observations. The most widely known of these is the Fabry-Perot interferometer which creates a spectrum for monochromatic light comprised of equal area rings at the infinity focus of an objective lens system. The circular interference patterns must be analyzed quantitatively to extract the information provided by the optical instrument.
A number of complex scanning strategies have been developed to extract the information from the circular interference pattern. One known technique includes the "pinhole" scan which is accomplished by varying the etalon optical path either by changing the index of refraction, or by actually moving the plates. More recently, complex image plane detectors which have an anode structure which matches the fringe pattern have been produced. There is a need, however, for a system which simplifies the analysis of interferometric information by converting the information in the circular rings to a pattern which easily can be analyzed, as is the case with the conventional spectrometer, while retaining the technical and other advantages of an interferometer.
It is, therefore, an object of this invention to provide a simple and economical system for analyzing circular fringe information produced by an interferometer.
It is another object of this invention to improve the resolution with which circular fringe information from an interferometer can be analyzed.
It is also an object of this invention to provide a system for monitoring and analyzing circular fringe information using a linear array detector.
It is a further object of this invention to provide a system which is efficient in its employment of circular fringe energy during analysis of the information contained therein.